This work is aimed at exploring regulatory mechanisms involved in normal differentiation and malignant transformation, using the B16 melanoma model system involving melanotic, amelanotic malignant clones, and amelanotic nonmalignant clones derived from the melanotic clone after continuous growth in the presence of one microgram of 5-bromodeoxyuridine [BrdUrd] per ml. The BrdUrd clone C[unreadable]3[unreadable]471 immunizes syngeneic mice against the parental tumor. The leukocyte subpopulations elicited by immunization with BrdUrd clone C[unreadable]3[unreadable]471 include macrophages, T cells, and possibly natural killer cells, which cooperate in rejection of the tumorigenic parental melanoma clone (B[unreadable]5[unreadable]59). We have isolated and grown T lymphocytes from normal mice immunologically stimulated with BrdUrd clone C[unreadable]3[unreadable]471. We have used this system to study the effects of human recombinant interleukin 2 (rIL-2, courtesy Cetus Corporation) with or without spleen cells from immunized mice on tumor-bearing mice. We have found that rIL-2 with or without immune spleen cells is highly effective in eradicating tumor when administered to mice previously implanted with the nonimmunogenic B16 parental tumor. IL-2 is most effective with early tumors and when a total of 10[unreadable]6[unreadable] Cetus units (5x10[unreadable]4[unreadable] per day) are administered in mice on alternate days for 5 weeks. Therapy with rIL-2 results in regression of almost 100% of early tumors when rIL-2 is inoculated close to the tumor site, i.e., subcutaneously (sc) with a tumor that is implanted sc and intraperitoneally (ip) with an ip tumor. We have also found that we can transfer selectable and unselectable genes into mouse melanoma clones using calcium phosphate coprecipitation. Frequencies of transferent colony formation with melanoma recipients approach or surpass mouse LTK[unreadable]-[unreadable] cells after treatment with either of two codominantly selectable plasmid vectors, pSV2gpt or pGCcos3neo. We applied this system successfully to DNA-mediated transfer of a gene specifying a 130,000 molecular weight glycoprotein (gp 130) from human melanoma cells to one of our mouse melanoma clones at a frequency of 3x10[unreadable]-4[unreadable]. By continuing these approaches we hope to increase our understanding of regulatory mechanisms in differentiation, and cellular and lymphokine interactions in immune surveillance. We also hope to work out protocols using IL-2 to effect tumor regression in mice which can be adapted to clinical use by other investigators. (M)